staging: comedi: ni_tio: make ni_tio_rinsn() a proper comedi (*insn_read)

Change the parameters to ni_tio_rinsn() to make is a proper comedi
(*insn_read) function. This allows using it directly and removing the
wrapper functions in the ni_660x and ni_mio_common modules.

For aesthetics, rename the function.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>